According to a certain digital communication technique, a video data signal can be transmitted along with a control signal over a single serial signal line in a computer system (see Patent Document 1).
At present, there are known protocols which achieve bidirectional communication of multimedia data over a single line. Examples of the protocols include a communication protocol for CEC (Consumer Electronics Control) as an optional standard in the digital interface standards HDMI (High-Definition Multimedia Interface), and a communication protocol called AV.Link (or Q-Link, etc., hereinafter collectively referred to as AV.Link) for control of a VCR from a TV (connection between SCART terminals), which is used on the European market.
Conventionally, for example, in order to achieve bidirectional communication using the AV.Link communication protocol, a timer function, an external interrupt function, and a port function, which are peripheral functions generally incorporated in an LSI, are used and controlled by a software process with a CPU.
Transmission is achieved by using the timer function to count a time defined by the standard, and in accordance with the timer interrupt, using the port output function to port-output “High” and “Low”. Reception is achieved by generating an external interrupt at an edge of an AV.Link signal input by the external interrupt function, and in accordance with the external interrupt, using the timer function to check whether or not the waveform is one that is defined by the standard and perform sampling of received data. Since the AV.Link communication is bidirectional communication, an additional circuit is required for performing bidirectional communication outside the LSI using two terminals of the LSI, i.e., a transmission port output terminal and a reception external interrupt input terminal. Arbitration monitoring during transmission is performed as follows. The transmission port output terminal and the reception external interrupt input terminal of the LSI are monitored in predetermined cycles using an interrupt of the timer function. When the two terminals have different states, transmission is changed to reception.
Patent Document 1: U.S. Pat. No. 6,151,334